In watercooled outboard motor systems, water is taken in through an inlet in the drive shaft housing, pumped through the water cooling passages in the motor block and cylinder head and then out of the motor, typically through the exhaust system. While the water inlet is designed to stop the ingestion of foreign matter into the system, small shells and other debris do sometimes get into the cooling water passage and can clog the water passage around the thermostatic control valve, particularly when the motor is operating at low power when less cooling water is required and the thermostatic control valve is more nearly closed.
Thermostatic flow control valves, well known in the art, open and close in response to the temperature of the water passing over the temperature sensing element of the valve.
All known prior art outboard motors that utilize a thermostatic valve to control the rate of flow of cooling water to control the temperature of the engine utilize a valve of relatively small diameter when compared to such valves utilized in larger four cycle automobile or marine engines. Such small diameter valves have been utilized in outboard motors because the range of movement of the valve stem renders them effective in maintaining the required flow of cooling water through the motor at all throttle settings in order to maintain the desired operating temperature of the motor.
One problem with these small diameter valves is that they are subject to being clogged by foreign matter entering the cooling water system through the water intake. The clogging results from the fact that these valves cannot open far enough to let the foreign matter pass through the flow control passage between the valve stem and seat. When the valve clogs, the flow of cooling water stops or is restricted, the motor overheats and can be damaged.
The primary objective of this invention is to provide a larger valve opening when the valve is obstructed by foreign matter and the temperature of the cooling water rises dangerously, to enable the foreign matter to pass through the thermostatic control valve and out of the cooling water system.
A further objective of the invention is to maintain consistent desired rates of cooling water flow through the motor during normal operation when the valve opening is not obstructed by foreign matter and thereby avoid undesired temperature fluctuations.